I Have Noticed A Marble-size Lump On The Upper Right

I have noticed a marble-size lump on the upper right side of my neck just below my jaw bone. This lump is only sometimes visible; most times it is very visible right after I have done my neck exercises. This lump can be pushed back into my neck and becomes virtually unnoticeable. I do not experience such a lump on the left side of my neck. Is this serious? What kind of specialist should I contact? Thank you YYYY@YYYY